Freeze-Thaw Damage to Brick in Middle Tennessee Homes

What is actually happening inside the brick

Fired clay brick is porous. Not sponge-like, but shot through with fine capillaries that hold water. Under a microscope a brick wall is a network of tiny reservoirs.

Water expands by roughly nine percent when it turns to ice. When a pore is full enough that the ice has nowhere to go, that expansion pushes outward on the pore walls. One cycle does nothing you can see. A few hundred cycles crack the structure between pores, and the outer face separates from the body behind it.

That is why spalling looks like the front of the brick fell off in a sheet. It did. The failure plane forms just behind the fired surface, where the pressure has been building for years.

Why our winter is harder than a colder one

Homeowners moving down from the Midwest expect masonry to fare better here. It often fares worse, and the reason has very little to do with how cold it gets.

What damages brick is the crossing, not the cold. A wall in Minnesota freezes hard in December and the water inside it stays ice until March. That is one crossing in an entire winter, and a wall on the Gulf coast never gets one at all. Middle Tennessee collects more of them than either, because our winter hovers around the freezing point instead of settling below it. A hard freeze overnight in Murfreesboro is routinely followed by an afternoon well above it, then another freeze that night. A wall that stays saturated here can cross the line dozens of times between December and February.

The other half of it is what our winter precipitation actually is. Snow mostly sits on a wall and blows off it. Rain soaks in. Around Rutherford County the standard pattern is a wet front and then a clear cold night behind it, which is exactly the order this mechanism needs. Fill the pores, then drop the temperature. Our walls go into most of their crossings already loaded.

So the number that matters is not the low a winter reached. It is how many times that winter crossed the line. Each crossing is one loading cycle on the same brick and they accumulate, which makes this a fatigue problem rather than a cold one. By that count Middle Tennessee is harder on masonry than places that freeze in December and do not thaw until spring.

No water, no damage

This is the part worth holding onto, because it is where the whole repair strategy comes from. Dry brick freezes harmlessly. Freeze-thaw damage requires the brick to be near saturation when the temperature drops.

So freeze-thaw is really a water management problem wearing a winter costume. Find where the wall is getting soaked and you have found the fix.

Gutters overflowing or discharging against the wall
Grade sloping back toward the foundation after a wet spell
Weep holes blocked by mulch, caulk or mortar droppings
A cracked chimney crown letting water into the stack from above
Sprinkler heads hitting the wall every morning through the winter
Horizontal surfaces with no wash: caps, sills, steps and wall tops

Where it turns up first

Damage concentrates in wet places, and the same short list appears on house after house around Murfreesboro and Smyrna.

Chimneys lead by a wide margin. A chimney is exposed on four sides, sits above the roof with nothing shading it, and takes rain from every direction. Then come the bottom courses near grade, where splash and soil contact keep brick damp. Then steps and treads, which hold standing water on purpose.

North and northeast faces get hit harder than sunny walls. They dry slowly, so they go into each freeze wetter than the rest of the house. If one elevation looks noticeably worse than the others, check which way it faces before assuming a defect.

Brick grade, salvage brick and the mortar question

Not all brick is made for this. Facing brick is manufactured to ASTM standards that distinguish between weathering exposures, and the severe weathering grade is what belongs on an exterior wall in a freeze-thaw climate. The Brick Industry Association publishes technical guidance on durability and exposure that any competent supplier will know.

This is where salvage brick catches people. Reclaimed interior brick, or soft old common brick pulled from a demolition, was never intended to face weather. It looks wonderful in a garden wall and it comes apart in about five winters.

Mortar matters just as much. Mortar harder than the brick it holds gives movement nowhere to go, so the brick takes the damage instead of the joint. On the older brick around the square this is the single most common way a repair makes a wall worse.

What actually stops it

Dry the wall out and the problem stops advancing. That means gutters, downspout extensions, grade, open weeps, a sound crown and repointed joints. Unglamorous, and it works.

What does not work is a film-forming sealer. Coating a brick wall that is already taking on water traps the moisture behind the film, and the next hard freeze pushes the face off with the sealer still attached. If a coating is being discussed at all, it should be a breathable one, applied after the water source is fixed, never instead of fixing it.

Two smaller habits help. Keep deicing salt off masonry steps and use sand for traction instead, since salt accelerates surface breakdown. And keep leaves and mulch pulled back from the base course so the bottom of the wall can dry between rains.

How the year is meant to run

Autumn is preparation. Clear the gutters, check the crown, pull mulch off the brick, and get soft joints repointed while the weather still allows it. That allowance runs out around forty degrees, and it runs out for the same reason the rest of this article exists. Green mortar is the wettest material on the wall, so the nine percent expansion that needs decades to break a brick will ruin a fresh joint in one night. The repair season closes just as the damage season opens. Work the calendar backward from that.

February and March are when the damage shows itself. New spalling, fresh sand at the base of a wall and popped faces all appear as the last cycles play out. That is the time to walk the house and take photographs.

Then repairs run from spring through autumn. Booking in early spring gets you ahead of the queue and gives the work a full dry season to cure before the next winter arrives.